Hot-melt adhesives are used extensively for case and carton sealing on automated packaging machinery. Inherent in hot-melt adhesive dispensers are the problems of soiling, drooling and stringing between applications. The typical solutions to these problems are the employment of (1) nozzle assemblies containing pressure activated valves such as that seen in U.S. Pat. No. 3,608,793 and/or (2) small diameter nozzle orifices. Both of these solutions require the use of high pressure equipment, either to insure activation of the valve or to supply a sufficient amount of adhesive to the carton flaps through the small diameter orifices. High pressure equipment is more expensive than that used in low pressure applications and at the same time it is potentially dangerous since a rupture in the equipment could spray melted adhesive in any direction.
The use of large orifices on the nozzles of low pressure equipment eliminates the problems of char particle clogging that result from degraded adhesive found in capillary nozzles and which necessitates use of filters with the high pressure apparatus. However, large diameter orifices may cause problems of drooling from the nozzle tips between applications because of the large volume of adhesive material past the cutoff valve. Decreasing the size of the bore of the passageway supplying adhesive to the nozzle tip would interfere with adequate adhesive flow under low pressure conditions. U.S. Pat. No. 3,348,520 and U.S. Pat. No. 3,608,793 are typical of prior art hot-melt adhesive dispensers used in the automated packaging industry. Both of these patents use high pressure equipment to initiate pressure-activated nozzle valves.
U.S. Pat. No. 3,981,123 shows a hot-melt adhesive apparatus which applies adhesive to the top and bottom flaps of a carton. A large portion of the elements that make up the apparatus are present only for the purpose of aligning the box for proper adhesive application. The apparatus must be realigned each time a different sized box enters the assembly line.
An object of the present invention was to provide a reliable, uncomplicated hot-melt adhesive dispenser for application on an automated assembly line.
A further object was to devise a multi-orifice nozzle assembly that could be used with low-pressure hot-melt adhesive dispensers and that would maintain clean nozzle cutoff between applications without drips, drools, or leaks from the nozzle tip.